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Noises Off (Bonus Material)

7/8/2008

DENOISE IN THE NAME OF THE LAW

Sometimes law-enforcement authorities will utilize broadband-noise reduction to make intelligible a recording of a witness, a suspect, or even a confession that''s obscured. In these so-called forensic audio situations, intelligibility is much more important than pristine sound quality, so more-extreme noise-reduction settings can be used. “It''s likely that the noise will be louder than the good signal,” says Enhancedaudio''s Curtis Crowe of the forensic audio world, “so that presents its own different challenge.”

Although most of Northeastern University professor Leon Janikian''s AR work has been in the vinyl transfer area, he''s been involved in forensic restoration work as well. “I''ve actually done a couple of murder cases,” says Janikian, “and in these cases, the perpetrator would have given the confession. In one case the confession was not well recorded, and it was considered inadmissible. The district attorney convinced the judge to try to get the recording restored, and somehow or other they found me.”

Using the Waves Restoration Bundle, Janikian denoised the upside-down confession audio, which he had to first strip from the videotape it was on. Denoising wasn''t enough in this circumstance, and he had to apply EQ, too. “I was boosting around 500 and then 2k to 3k,” remembers Janikian, “and I was rolling off some other stuff because it was as much removal as it was enhancement. Because if there''s some kind of high-pitched noise or background noise, you do no harm getting rid of that stuff.”

RESTORING THE PAST

Janikian, a former recording engineer of Armenian descent, is involved in a long-term project, transferring 78-rpm recordings of old Armenian music to Pro Tools. He says that getting the best possible transfer from vinyl to digital is helpful in reducing how much restoration work he''ll subsequently have to do on a particular file. “I have a Stanton turntable with a decent arm on it and I use a Stanton cartridge and many different styli,” he says. “So it will have many different radiuses. The standard is a 2.7 mil, then you get a larger one, 3.3. And you get a smaller one, 2.2, and a little smaller than that with a flat bottom. So you essentially ride the stylus—there''s usually a wear groove in the disk where most of the styli have ridden in the past. And that''s often the noisiest or the biggest problem.”

FIG. A: The highlighted wave on the left is a sample-level look at a click in iZotope RX. On the right is the same waveform after being fixed by RX''s Declicker tool.

FIG. A: The highlighted wave on the left is a sample-level look at a click in iZotope RX. On the right is the same waveform after being fixed by RX''s Declicker tool.

Once Janikian starts working on the file in Pro Tools, he''ll try to use as little audio-restoration processing as he can, in order to avoid sonic degradation. He''ll sometimes do separate passes on the declicking. “Sometimes it''s better to do a destructive AudioSuite pass a little bit mild, and then a real-time [nondestructive] one after that, because I don''t want to box myself in,” he says. He''ll often use the noise-monitoring feature of Waves X-Click or X-Crackle (the button labeled Difference) when dialing in his reduction settings. “What I try to do is to not hear any music as I adjust the click removal.” But the best results aren''t always achieved by limiting the reduction to the clicks and crackle without touching the target music. “Once in a while I''ll choose to even take away a little music,” he says.

CLICK AWAY

Audio anomalies like clicks and pops are sometimes more easily excised on an individual basis rather than with a global application of removal software. By zooming in to the sample level (or sometimes not quite that far), you can usually isolate a stray problem (clicks typically look like spikes in the waveform display; see Fig. A), which can then be ameliorated using an AR plug-in or simply cut or attenuated. The steps are relatively simple: zoom, select, monitor, and process. If you don''t have a click remover in your software, you can use pencil-tool editing to redraw the waveform at the point of the click, assuming your host software supports that.

Pops are often the results of bad edits and can be fixed by moving the edit point to a zero-crossing. (For more about this type of editing, see the waveform-editing sections of “Producing Pro Podcasts” in the December 2007 issue of EM, available at emusician.com/tutorials/emusic_producing_pro_podcasts/index.html.)

If you''re working in a film or video soundtrack, be careful about deleting audio destructively (especially if you''re working in a 2-track editor), because that will change the duration of the track and likely throw it out of sync with the visual content. If you have an audio anomaly that you need to get rid of, attenuating it out completely is the better solution.

For plosives (loud p or b sounds), I''ve found that selecting the p or b sound only (audition it to be sure) and then applying about a 10 to 15 dB cut to it will get rid of its problem aspects while leaving enough of it to ensure that the word still sounds correct.

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